This application relates to methods for synthesizing zeolites using alcohols and/or diols in the reaction mixtures for forming the zeolites.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by x-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of large dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties.
Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline aluminosilicates. These aluminosilicates can be described as rigid three-dimensional frameworks of SiO.sub.4 and AlO.sub.4 in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing aluminum is balanced by the inclusion in the crystal of a cation, for example, an alkali metal or an alkaline earth metal cation. This balanced electrovalence can be expressed by a formula wherein the ratio of aluminum to the number of various cations, such as Ca/2, Sr/2, Na, K or Li is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given aluminosilicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. These zeolites have come to be designated by zeolite A (U.S. Pat. No. 2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat. No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4 (U.S. Pat. No. 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886), zeolite ZSM-11 (U.S. Pat. No. 3,709,979) and zeolite ZSM-12 (U.S. Pat. No. 3,832,449), merely to name a few.
Although the term, zeolites, encompasses materials containing silica and alumina, it is recognized that the silica and alumina portions may be replaced in whole or in part with other oxides. More particularly, GeO.sub.2 is an art recognized substitute for SiO.sub.2. Also, B.sub.2 O.sub.3, Cr.sub.2 O.sub.3, Fe.sub.2 O.sub.3, and Ga.sub.2 O.sub.3 are art recognized replacements for Al.sub.2 O.sub.3. Accordingly, the term zeolite as used herein shall connote not only materials containing silicon and, optionally, aluminum atoms in the crystalline lattice structure thereof, but also materials which contain suitable replacement atoms for such silicon and/or aluminum. On the other hand, the term aluminosilicate zeolite as used herein shall define zeolite materials consisting essentially of silicon and aluminum atoms in the crystalline lattice structure thereof, as opposed to materials which contain substantial amounts of suitable replacement atoms for such silicon and/or aluminum.
The entire disclosures of the above-mentioned U.S. patents are also expressly incorporated herein by reference.
The synthesis methods described hereinafter are especially applicable to the preparation of the particular zeolites, ZSM-22 and ZSM-23. The crystal structures of ZSM-22 and ZSM-23 are closely related in that both zeolites contain structurally identical subunits which generate noninterpenetrating one-dimensional channels defined by 10-rings which are parallel to the short axis of the lattice parameter. The 10-ring channel dimensions in ZSM-22 and ZSM-23 are very similar, though subtle differences exist in the shapes of the openings. The structure of ZSM-22 is described in more detail in an article by Kokotailo et al entitled, "The Framework Topology of ZSM-22: A High Silica Zeolite" appearing in ZEOLITES, 1985, Vbl. 5, November at pages 349-351. The structure of ZSM-23 is described in more detail in an article by Rohrman et al entitled, "The Framework Topology of ZSM-23: A High Silica Zeolite" also appearing in the same journal, i.e., ZEOLITES, 1985, Vol. 5, November, at pages 352-354.
Crystalline silicate ZSM-23 and its preparation, e.g. from a reaction mixture containing pyrrolidine directing agent, are taught by U.S. Pat. No. 4,076,842, the entire disclosure of which is incorporated herein by reference. ZSM-23 has a distinctive X-ray diffraction pattern which distinguishes it from other known crystalline silicates. Synthesis of crystalline silicate ZSM-23 from a reaction mixture containing hexamethyl-diquaternary ammonium with a saturated or unsaturated C.sub.7 bridge hydrocarbon moiety as directing agent is taught in U.S. Pat. Nos. 4,490,342 and 4,619,820, the entire disclosures of which are expressly incorporated herein by reference. The diquaternary used in synthesis of ZSM-23 in the latter is shown in U.S. Pat. No. 4,531,012.
Zeolite KZ-1, having the structure of ZSM-23, is shown in Zeolites, 1983, Vol. 3, pages 8-10, to be synthesized from a reaction mixture containing pyrrolidine, 2-aminopropane or dimethylamine, silica, aluminum sulfate and sodium hydroxide.
U.S. Pat. No. 4,296,083 claims synthesizing zeolites characterized by a Constraint Index of 1 to 12 and an alumina/silica mole ratio of not greater than 0.083 from a specified reaction mixture containing an organic nitrogen-containing cation, depending upon the particular zeolite desired, provided by, for example, an amine identified as being selected from the group consisting of triethylamine, trimethylamine, tripropylamine, ethylenediamine, propanediamine, butanediamine, pentanediamine, hexanediamine, methylamine, ethylamine, propylamine, butylamine, dimethylamine, diethylamine, dipropylamine, benzylamine, aniline, pyridine, piperidine and pyrrolidine.
U.S. Pat. No. 4,112,056 teaches synthesis of ZSM-23 with a pyrrolidine directing agent by adding a source of aluminum ions to a silica-rich amorphous reaction mixture at a rate whereby the aluminum ion concentration in the reaction mixture amorphous phase is maintained at steady state during crystallization. U.S. Pat. No. 4,497,786 shows treatment of zeolites, for example ZSM-23, following crystallization by increasing the temperature, e.g. cooking the crystals, to deagglomerate them.
U.S. Pat. No. 4,341,748 shows synthesis of ZSM-5 or ZSM-11 from reaction mixtures comprising, for example, ethanol, ZSM-5 or ZSM-11 seeds, ethanol and seeds, ethanol and ammonimum hydroxide, and ethanol, ammonimum hydroxide and seeds.
U.S. Pat. No. 4,104,151 shows organic compound conversion over catalyst comprising ZSM-23 prepared as in U.S. Pat. No. 4,076,842, above. U.S. Pat. Nos. 4,222,855; 4,575,416 and 4,599,162 teach dewaxing reactions over ZSM-23 catalyts. Aromatics alkylation, e.g. ethylbenzene synthesis, over catalyst comprising, for example, ZSM-23 is demonstrated in U.S. Pat. Nos. 4,547,605 and 4,107,224. ZSM-23 prepared in usual fashion and with an amorphous precipitated silica source of silicon for xylene isomerization is shown in U.S. Pat. No. 4,599,475. A combination process for conversion of olefins to high VI lubes, where the ZSM-23 catalyst component is synthesized from a reaction mixture containing a pure silica, is taught in U.S. Pat. No. 4,524,232.
Other catalytic uses of ZSM-23 include conversion of cumene to acetone and phenol (U.S. Pat. No. 4,490,566), dewaxing (U.S. Pat. Nos. 4,372,839 and 4,428,865), dewaxing hydrocrackate to make lube oil (U.S. Pat. No. 4,414,097), toluene disproportionation (U.S. Pat. No. 4,160,788), selective production of p-substituted benzene (U.S. Pat. No. 4,100,217) and selective production of p-xylene (U.S. Pat. No. 4,049,738).
As discussed in the above-mentioned article by Rohrman et al regarding the structure of ZSM-23, a zeolite designated as ISI-4 has the same topology as ZSM-23. Published European Patent Application Publication No. 102497 describes the synthesis of ISI-4 from an aqueous reaction mixture comprising (a) a silica source, (b) an alumina source, (c) an alkali metal and/or an alkaline earth metal source, and (d) ethylene glycol or (e) monoethanolamine.
ZSM-22 is described in U.S. Pat. No. 4,556,477, as well as in published European Patent Application Publication No. 102716. This EPA 102716 describes the preparation of ZSM-22 from reaction mixtures containing alkane diamines such as 1,6-hexanediamine. In such preparations, EPA 102716 indicates that potassium cations in the reaction mixture permit the synthesis of ZSM-22 having a silica/alumina ratio of less than 90, whereas sodium ions are preferably used in reaction mixtures capable of forming ZSM-22 at silica/alumina ratios of 90 and above. Note the paragraphs bridging pages 8 and 9 of this EPA 102716.
As pointed out in the above-mentioned article by Kokotailo et al regarding the structure of ZSM-22, zeolites designated as Nu-10 and ISI-1 each have the same framework topology as ZSM-22. Published European Patent Application Publication No. 77624 states that Nu-10 can be prepared from a reaction mixture comprising at least one organic compound of the formula: EQU L.sup.1 --(CH.sub.2).sub.n --L.sup.2
wherein each of L.sup.1 and L.sup.2, independently, represents a hydroxyl or an optionally substituted amino group and is an integer from 2 to 20, provided that when both L.sup.1 and L.sup.2 are optionally substituted amino groups n is an integer from 6 to 20. Examples 22 and 24 of this EPA 77624 describe the preparation of Nu-10 from a reaction mixture containing 1,6-hexanediol. Published European Patent Application Publication No. 87017 describes the addition of large amounts of methanol to aqueous mixtures to produce the zeolite designated as ISI-1.
One aspect of the present application involves reducing the crystallite size of zeolites. All other things being equal, zeolites of smaller crystallite size tend to have greater initial catalytic activity and tend to maintain activity longer during catalytic processes, particularly with regard to blockage of pores by coke. The effect of crystallite size on zeolite activity is especially pronounced in the case of medium pore size zeolites, such as ZSM-22 and ZSM-23, having unidirectional, nonintersecting channel systems. In accordance with an aspect of the present application, alcohols and/or diols are used in reaction mixtures in order to enable the production of zeolites of reduced crystallite size.
Alcohols and diols have been used in zeolite syntheses for purposes other than reduction of zeolite crystallite size. For example, U.S. Pat. Nos. 4,175,114 and 4,199,556 describe production of ZSM-5 and ZSM-11 by replacing organic nitrogen compounds with seeds of the desired zeolite and alcohol, mixtures of zeolite seeds with ammonium hydroxide, and/or alcohol or mixtures of the alcohol with ammonium hydroxide to substantially reduce the amount of organic ammonium cation usually present in the zeolite. The zeolite product can be exchanged directly without any calcination. Other publications which describe the use of alcohols and/or diols in the synthesis of zeolites include the above-mentioned EPA 77624, EPA 102497 and EPA 87017.
The addition of organic nitrogen containing compounds to reaction mixtures has been known to influence or direct the synthesis of certain particular zeolites. However, a particular organic nitrogen-containing compound can direct the synthesis of more than one zeolite depending on other synthesis parameters such as the silica/alumina ratio of the reaction mixture and the temperature of the crystallization. For example, in an article by Araya and Lowe, entitled "A Partial Determination of the Stability Fields of Ferrierite and Zeolites ZSM-5, ZSM-48 and Nu-10 K.sub.2 O--Al.sub.2 O.sub.3 --SiO.sub.2 --NH.sub.2 [CH.sub.2 ].sub.6 NH.sub.2 System" appearing in J. Chem. Res. Synop, No.6, (1985) at pages 192-193, it is pointed out that 1,6-hexanediamine can promote the synthesis of four different zeolites, e.g. depending upon the SiO.sub.2 /Al.sub.2 O.sub.3 ratio of the reaction mixture. FIG. 2 of the article by Araya and Lowe points out that 1,6-hexanediamine, when used in a particular reaction mixture, promotes the synthesis of Nu-10 over a very narrow window of SiO.sub.2 /Al.sub.2 O.sub.3 in the reaction mixture. However, as the SiO ratio decreases, a transition to ZSM-5 takes place whereby increasing amounts of ZSM-5 form along with Nu-10 until the Nu-10 component becomes undetectable. Furthermore, as shown in FIG. 1 of the Araya and Lowe article, when the crystallization temperature for this particular reaction system is reduced from 180.degree. C to 150.degree. C, pure Nu-10 is not produced, but Nu-10 is instead always produced in admixture with ZSM-5.
Accordingly, it would be desirable to improve synthesis techniques in order to produce zeolites such as ZSM-22 at relatively low temperatures and at relatively low silica/alumina ratios without coproducing ZSM-5.
The entire disclosures of the above-mentioned publications, including articles and U.S. Patents, discussed in this BACKGROUND section, are expressly incorporated herein by reference.